MAAS API calls with an empty POST envelope fails

Any MAAS API call using with a POST method sending a valid, but empty, post "envelope" of multipart/form-data in its body will fail, even if no body data is required for that particular call. Note that there are no actual fields in the form-encoded data, just the empty boundaries.

This envelope can be added automatically by generic client HTTP libraries and is also by libpython3-maas.

On failures, MAAS returns no error: request just times out.

Follows transcriptions of failing and working HTTP requests running against an production MAAS 2.9.2 (9164-g.ac176b5c4). There are also unmodified tcpdump captures of both of them attached. Is *not* possible to "replay" these requests for testing, however, as the API keys used were added only for the test and already removed.

Failing request, using with by python-libmaas as client library/abstraction layer.

POST /MAAS/api/2.0/machines/ryrfeb/?op=release HTTP/1.1
Host: 10.228.68.5:5240
User-Agent: Python-urllib/3.8
Content-Type: multipart/form-data; boundary="===============3556993604024216494=="
Mime-Version: 1.0
Content-Length: 82
Authorization: OAuth oauth_nonce="146966075862726036601614173740", oauth_timestamp="1614173740", oauth_version="1.0", oauth_signature_method="PLAINTEXT", oauth_consumer_key="MpwT8pwxVTqELehyea", oauth_token="q7kzPjbrX93PfCtHu2", oauth_signature="%266gb8eQ7qFtPuQqnDqREPfb9EZu4ybsgq"
Accept-Encoding: gzip
Connection: close

--===============3556993604024216494==

--===============3556993604024216494==--

Working request generated with python-requests (no abstraction layer).

POST /MAAS/api/2.0/machines/ryrfeb/?op=release HTTP/1.1
Host: 10.228.68.5:5240
User-Agent: python-requests/2.25.1
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 0
Authorization: OAuth oauth_nonce="162269732045930448861614173158", oauth_timestamp="1614173158", oauth_version="1.0", oauth_signature_method="PLAINTEXT", oauth_consumer_key="MpwT8pwxVTqELehyea", oauth_token="q7kzPjbrX93PfCtHu2", oauth_signature="%266gb8eQ7qFtPuQqnDqREPfb9EZu4ybsgq"

HTTP/1.1 200 OK
Server: TwistedWeb/18.9.0
Date: Wed, 24 Feb 2021 13:25:58 GMT
Content-Type: application/json; charset=utf-8
Vary: Authorization, Cookie, Accept-Encoding
X-Maas-Api-Hash: 815b645be0437854a58b51e2d1deb0f27266dd8e
X-Frame-Options: SAMEORIGIN
Content-Length: 2654
Content-Encoding: gzip

(... returned data removed ...)